Electric potential at a point would be the work done to [in a case with a positive test charge and negative electric field] lift the particle from that point to infinitely far away. The coulomb force is defined as inversely proportional to the distance of separation, so if you were to have them both somehow "stacked" in the exact same point in space [ignoring the fact they're fermions] I'm not entirely sure how it would even be possible to separate them. I think that Equation blows up for good reason.
Furthermore, to illustrate my point in a bit clearer of a way, if you release something in a potential and exert no other forces on it, it'll move to minimise that potential energy. Where would a charge move if you put it exactly on top of another, such that the points of their charges were exactly the same.